The invention relates to a circuit arrangement for limiting the switch-on current and for providing an over voltage protection in switch mode power supply devices.
Switch mode power supply arrangements generally include, in the input circuit, a comparatively large capacitance, normally formed by an electrolytic capacitor. This capacitance serves as a low-ohmic source for the primary-side pulse currents of the converter circuit and, together with a series-connected inductance of a input filter, is fundamentally responsible for the level and form of the switch-on current.
The charging current which flows into the storage capacitor when the power supply device in question is plugged-in or switched-on, can trigger series-connected fuses and in the case of plug-in power supply devices can destroy the plug pins when the device, in the form of a slide-in module, insert module or plug-in assembly, become live.
It is also normal practice to subject power supply devices of the type referred to in the introduction to a test in which the power supply device is supplied at its input with voltage pulses of a specific form and level. These pulses can destroy sensitive components, such as for example semiconductors.